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1. Mapping Groundwater Recharge Potential in High Latitude Landscapes Using Public Data, Remote Sensing, and Analytic Hierarchy Process

   https://doi.org/10.3390/rs15102630  

   Guerrón-Orejuela, Edgar J.; Rains, Kai C.; Brigino, Tyelyn M.; Kleindl, William J.; Landry, Shawn M.; Spellman, Patricia; Walker, Coowe M.; Rains, Mark C. (May 2023, Remote Sensing)

   Understanding where groundwater recharge occurs is essential for managing groundwater resources, especially source-water protection. This can be especially difficult in remote mountainous landscapes where access and data availability are limited. We developed a groundwater recharge potential (GWRP) map across such a landscape based on six readily available datasets selected through the literature review: precipitation, geology, soil texture, slope, drainage density, and land cover. We used field observations, community knowledge, and the Analytical Hierarchy Process to rank and weight the spatial datasets within the GWRP model. We found that GWRP is the highest where precipitation is relatively high, geologic deposits are coarse-grained and unconsolidated, soils are variants of sands and gravels, the terrain is flat, drainage density is low, and land cover is undeveloped. We used GIS to create a map of GWRP, determining that over 83% of this region has a moderate or greater capacity for groundwater recharge. We used two methods to validate this map and assessed it as approximately 87% accurate. This study provides an important tool to support informed groundwater management decisions in this and other similar remote mountainous landscapes. 

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2. Modeling groundwater responses to climate change in the Prairie Pothole Region

   https://doi.org/10.5194/hess-2019-155  

   Zhe Zhang, Yanping Li1 (April 2019, Hydrology and earth system sciences discussions)

   Shallow groundwater in the Prairie Pothole Region (PPR) is recharged predominantly by snowmelt in the spring and may supply water for evapotranspiration through the summer/fall. This two-way exchange is underrepresented in land-surface models. Furthermore, the impacts of climate change on the groundwater recharge are uncertain. In this paper, we use a coupled land and groundwater model to investigate the hydrologic cycle of shallow groundwater in the PPR and study its response to climate change at the end of the 21st century. The results show that the model reasonably simulates the water table depth (WTD) and the timing of recharge processes, but underestimates the seasonal variation of WTD, due to mismatches of the soil types between observations and the model. The most significant change under future climate occurs in the winter, when warmer temperature changes the rain/snow partitioning, delay the time for snow accumulation/soil freezing while bring forward early melting/thawing. Such changes lead to an earlier start to a longer recharge season, but with lower recharge rates. Different signals are shown in the eastern and western PPR in the future summer, with reduced precipitation and drier soils in the east but little change in the west. The annual recharge increased by 25% and 50% in the eastern and western PPR, respectively. Additionally, we found the mean and seasonal variation of the simulated WTD are sensitive to soil properties and fine-scale soil information is needed to improve groundwater simulation on regional scale. 

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3. Influence of Shallow Groundwater Evapotranspiration on Recharge Estimation Using the Water Table Fluctuation Method

   https://doi.org/10.1029/2022WR032073  

   Boumis, Georgios; Kumar, Mukesh; Nimmo, John R.; Clement, T. Prabhakar (October 2022, Water Resources Research)

   Abstract Groundwater recharge moves downward from the land surface and reaches the groundwater to replenish aquifers. Despite its importance, methods to directly measure recharge remain cost and time‐intensive. Recharge is usually estimated using indirect methods, such as the widely used water‐table fluctuation (WTF) method, which is based on the premise that rises in groundwater levels are due to recharge. In the WTF method, recharge is calculated as the difference between the observed groundwater hydrograph and the hydrograph obtained in the absence of water input. The hydrograph in the absence of rise‐producing input is estimated based on a characteristic master recession curve (MRC), which describes an average behavior for a declining water‐table. Previous studies derive MRC using recession data from all seasons. We hypothesize that for sites where groundwater table is shallow, using recession data from periods with high groundwater‐influenced evapotranspiration (ET) rates versus all periods will yield significantly different MRC, and consequently different estimates of recharge. We test this hypothesis and show that groundwater recession rates are significantly greater in warm months when the groundwater‐influenced ET rates are higher. Since obtaining seasonal recession rates is challenging for locations with a limited amount of data and is prohibitive if it is to be obtained for any given season of a particular year, we propose two novel parsimonious methods to obtain recession time constants for distinct seasons. The proposed methods show the potential to significantly improve the estimates of seasonal recession time constants and provide a better understanding of seasonal variations in recharge estimates. 

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4. Combined impacts of uncertainty in precipitation and air temperature on simulated mountain system recharge from an integrated hydrologic model

   https://doi.org/10.5194/hess-26-1145-2022  

   Schreiner-McGraw, Adam P.; Ajami, Hoori (January 2022, Hydrology and Earth System Sciences)

   Abstract. Mountainous regions act as the water towers of the worldby producing streamflow and groundwater recharge, a function that isparticularly important in semiarid regions. Quantifying rates of mountainsystem recharge is difficult, and hydrologic models offer a method toestimate recharge over large scales. These recharge estimates are prone touncertainty from various sources including model structure and parameters.The quality of meteorological forcing datasets, particularly in mountainousregions, is a large source of uncertainty that is often neglected ingroundwater investigations. In this contribution, we quantify the impact ofuncertainty in both precipitation and air temperature forcing datasets onthe simulated groundwater recharge in the mountainous watershed of theKaweah River in California, USA. We make use of the integrated surface water–groundwater model, ParFlow.CLM, and several gridded datasets commonly usedin hydrologic studies, downscaled NLDAS-2, PRISM, Daymet, Gridmet, andTopoWx. Simulations indicate that, across all forcing datasets, mountain front recharge is an important component of the water budget in themountainous watershed, accounting for 9 %–72 % of the annual precipitation and ∼90 % of the total mountain system recharge to theadjacent Central Valley aquifer. The uncertainty in gridded air temperatureor precipitation datasets, when assessed individually, results in similarranges of uncertainty in the simulated water budget. Variations in simulatedrecharge to changes in precipitation (elasticities) and air temperature(sensitivities) are larger than 1 % change in recharge per 1 % change inprecipitation or 1 ∘C change in temperature. The total volume ofsnowmelt is the primary factor creating the high water budget sensitivity, and snowmelt volume is influenced by both precipitation and air temperatureforcings. The combined effect of uncertainty in air temperature andprecipitation on recharge is additive and results in uncertainty levels roughly equal to the sum of the individual uncertainties depending on thehydroclimatic condition of the watershed. Mountain system recharge pathwaysincluding mountain block recharge, mountain aquifer recharge, and mountainfront recharge are less sensitive to changes in air temperature than changesin precipitation. Mountain front and mountain block recharge are moresensitive to changes in precipitation than other recharge pathways. Themagnitude of uncertainty in the simulated water budget reflects theimportance of developing high-quality meteorological forcing datasets in mountainous regions. 

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5. Implications for groundwater recharge from stable isotopic composition of precipitation in Hawai'i during the 2017–2018 La Niña

   https://doi.org/10.1002/hyp.13907  

   Dores, Daniel; Glenn, Craig R.; Torri, Giuseppe; Whittier, Robert B.; Popp, Brian N. (September 2020, Hydrological Processes)

   Abstract The project captured a subset of the hydrological cycle for the tropical island of O'ahu, linking precipitation to groundwater recharge and aquifer storage. We determined seasonal storm events contributed more to aquifer recharge than year‐round baseline orographic trade wind rainfall. Hydrogen and oxygen isotope values from an island‐wide rain collector network with 20 locations deployed for 16 months and sampled at 3‐month intervals were used to create the first local meteoric water line for O'ahu. Isotopic measurements were influenced by the amount effect, seasonality, storm type, and La Niña, though little elevation control was noted. Certain groundwater compositions from legacy data showed a strong similarity with collected precipitation from our stations. The majority of these significant relationships were between wet season precipitation and groundwater. A high number of moderate and heavy rainfall days during the dry season, large percentage of event‐based rainfall, and wind directions outside of the typical NE trade wind direction were characteristics of the 2017–2018 wet season. This indicates that the majority of wet season precipitation is from event‐based storms rather than typical trade wind weather. The deuterium‐excess values provided the strongest evidence of a relationship between groundwater and different precipitation sources, indicating that this may be a useful metric for determining the extent of recharge from different rain events and systems. 

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